Have you tried printing the top sheet to see whether it makes things better or worse once ink is applied? I'm still using my older stock so I haven't come across this yet.
Nothing to lose but a bit of ink. I asked just in case the ink may mask the problem - if so the paper would of course be usable.
Printing does mask the problem, but whether you can see it or not depends how hard you look. I wouldn't sell it to anyone, but it's good enough for a proof that would eventually be thrown out anyway.